Image sensing device, image reading device, image forming apparatus and image sensing method

ABSTRACT

An image sensing device includes a plurality of photoelectric conversion elements arranged in one direction for each color of received light, and an analog-digital (AD) convertor that performs analog-digital conversion for each pixel group configured by a plurality of photoelectric conversion elements selected from the photoelectric conversion elements. The AD converter is disposed in a position adjacent to each of the photoelectric conversion elements configuring the pixel group.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by referencethe entire contents of Japanese Patent Application No. 2013-256248 filedin Japan on Dec. 11, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image sensing device, an imagereading device, an image forming apparatus and an image sensing method.

2. Description of the Related Art

Charge-coupled device (CCD) image sensors have been used as aphotoelectric conversion device for a scanner that reads an image inmany cases. However, because of an increasing demand for low powerconsumption, complementary metal-oxide-semiconductor (CMOS) linearsensors are gaining more attention. A CMOS linear sensor convertsincident light into electric charge by using photodiodes as in the caseof a CCD image sensor. The CCD image sensor converts electric chargetransferred by a shift register into voltage at a charge detector. TheCMOS linear sensor converts electric charge into voltage signals atcharge detectors provided for respective pixels and outputs the voltagesignals via switches. By this configuration, the CMOS linear sensorconsumes less power than the CCD image sensor.

The conventional CMOS linear sensors have a long analog bus connectingall the pixels to transfer analog image signals through the analog bus.Thus, wire resistance and wire capacitance are so large that theconventional CMOS linear sensors cannot achieve enhanced speed.

Japanese Patent Application Laid-open No. 2009-296544 describes sensorsthat scan three divided blocks, and each block is scanned three times toscan a whole line. The sensors simultaneously scan the divided blocks ora first block, a second block, and a third block in different colors inthe first scan, the second scan, and the third scan.

However, the conventional CMOS linear sensor cannot achieve enhancedspeed because of the difficulty in reducing wire resistance or wirecapacitance along the analog bus.

Therefore, it is desirable to provide an image sensing device, an imagereading device, an image forming apparatus, and an image sensing methodthat can achieve high-speed image reading.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an aspect of the present invention, there is provided animage sensing device including: a plurality of photoelectric conversionelements arranged in one direction for each color of received light; andan analog-digital (AD) converter that performs analog-digital conversionfor each pixel group configured by a plurality of photoelectricconversion elements selected from the photoelectric conversion elements,the AD converter being disposed in a position adjacent to each of thephotoelectric conversion elements configuring the pixel group.

According to another aspect of the present invention, there is providedan image sensing method performed by an image sensing device including aplurality of photoelectric conversion elements arranged in one directionfor each color of received light, the method including performing, by ananalog-digital (AD) converter, analog-digital conversion for each pixelgroup configured by a plurality of photoelectric conversion elementsselected from the photoelectric conversion elements, the AD converterbeing disposed in a position adjacent to each of the photoelectricconversion elements configuring the pixel group.

According to still another aspect of the present invention, there isprovided an image sensing device including: a plurality of photoelectricconversion means arranged in one direction for each color of receivedlight; and an analog-digital (AD) conversion means for performinganalog-digital conversion for each pixel group configured by a pluralityof photoelectric conversion means selected from the plurality ofphotoelectric conversion means, the AD conversion means being disposedin a position adjacent to each of the plurality of photoelectricconversion means configuring the pixel group.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an outline of an image reading device;

FIG. 2 is a timing chart illustrating operations for driving a CMOSlinear sensor illustrated in FIG. 1;

FIG. 3 is a diagram illustrating an example of a configuration outlineof an image sensing device according to a first embodiment of thepresent invention;

FIG. 4 is a diagram illustrating a configuration of pixels illustratedin FIG. 3;

FIG. 5 is a diagram illustrating the periphery of an analog-digital (AD)converter that converts analog signals output from the pixelsillustrated in FIG. 3 into digital signals;

FIG. 6 is a timing chart illustrating operations for driving the imagesensing device;

FIG. 7 is a schematic diagram illustrating colors of an image read andreproduced by the image sensing device;

FIG. 8 is a diagram illustrating an example of a configuration outlineof an image sensing device according to a second embodiment of thepresent invention;

FIG. 9 is a diagram illustrating a configuration of pixels illustratedin FIG. 8;

FIG. 10 is a diagram illustrating the periphery of an AD converter thatconverts analog signals output from the pixels illustrated in FIG. 8into digital signals;

FIG. 11 is a schematic diagram illustrating colors of an image read andreproduced by the image sensing device;

FIG. 12 is a diagram illustrating an example of a configuration outlineof an image sensing device according to a third embodiment of thepresent invention;

FIG. 13 is a diagram illustrating the periphery of an AD converter thatconverts analog signals output from pixels illustrated in FIG. 12 intodigital signals;

FIG. 14 is a timing chart illustrating operations for driving the imagesensing device;

FIG. 15 is a diagram illustrating an example of a configuration outlineof an image sensing device according to a fourth embodiment of thepresent invention;

FIG. 16 is a diagram illustrating a configuration of pixels illustratedin FIG. 15;

FIG. 17 is a diagram illustrating the periphery of an AD converter thatconverts analog signals output from the pixels illustrated in FIG. 15into digital signals;

FIG. 18 is a timing chart illustrating operations for driving the imagesensing device;

FIG. 19 is a diagram illustrating a configuration outline of a CMOS areasensor according to a comparative example; and

FIG. 20 is a diagram illustrating an outline of an image formingapparatus including an image reading device including, for example, animage sensing device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Described first is the background of the present invention. FIG. 1 is adiagram illustrating an outline of an image reading device 1. The imagereading device 1 includes a CMOS linear sensor 10, an analog front end(AFE) 12, and a timing generator (TG) 14.

The CMOS linear sensor 10 includes n pixels each including a photodiode(PD: photoelectric conversion element) 100, a charge detector (Cfd) 102,and a switch (SW) 104, and outputs image signals via an output buffer106. The PD 100 converts reflected light (incident light) from, forexample, a document into electric charge. The charge detector 102converts the electric charge accumulated in the PD 100 by thephotoelectric conversion into a voltage signal. An image signalconverted into a voltage signal is input to an analog bus via the switch104 and is output from the output buffer 106.

Specifically, the switches 104 are sequentially turned on from the firstpixel to the nth pixel to output image signals of the respective pixels.The CMOS linear sensor 10 contains, for example, approximately 7000pixels (n≈7000) to read an A3 document. The following descriptionassumes n=7000.

Drive signals (S) that drive the switches 104 are turned on once in oneline period. Because the drive signals cannot activate a plurality ofpixels at the same time, the drive signals activate the respectivepixels at slightly different timings. In other words, a signal(S[7000:1]) that drives each switch 104 is asserted once every pixelperiod in one line period, and the number of signals is equal to thenumber of pixels.

In the same manner, a signal (TS[7000:1]) that transfers the electriccharge accumulated in the PD 100 to the charge detector 102, and asignal (RS[7000:1]) that resets the charge detector 102 are assertedonce every pixel period in one line period, and the number of signals isequal to the number of pixels.

In FIG. 1, only one pixel each is illustrated in Pix1 to Pix(n) that arepixel positions on a readout subject. To output electric signals inthree RGB colors by converting incident light using filters in the threeRGB colors, pixels in the three colors (approximately 7000 pixels×threecolors) are arranged in arrays, each row of which contains pixels in thesame color.

The AFE 12 includes, for example, an analog-digital (AD) converter (ADC)120, and converts analog image signals output from the CMOS linearsensor 10 into digital image signals. The AFE 12 may include ahigh-speed serial signal converter (for example, low-voltagedifferential signaling (LVDS) or V-by-One HS) that transfers theconverted digital image signals to an image processing unit at thefollowing stage. The timing generator 14 outputs, for example, controlsignals that control the CMOS linear sensor 10 and signals that controlthe AFE 12.

The AFE 12 and the timing generator 14 may be configured in one chip, orthe CMOS linear sensor 10, the AFE 12, and the timing generator 14 maybe configured in one chip. The CMOS linear sensor 10 may include largerswitches 104 provided for respective pixels to achieve high-speed drive,and may include a broader analog bus to reduce the impedance and preventsignal degradation due to the high-speed drive. In this case, however,loads on the CMOS linear sensor 10 are inevitably increased caused byparasitic capacitance in the switches 104 and wire capacitance in theanalog bus, which may result in preventing the high-speed drive.

FIG. 2 is a timing chart illustrating operations for driving the CMOSlinear sensor 10 illustrated in FIG. 1. Drive signals for the CMOSlinear sensor 10 are generated by the timing generator 14 by using areference clock (CLK).

The timing generator 14 turns on a reset signal (RS) before starting ona line (before starting reading operation on each line). The RS resetselectric charge in the charge detector 102. The reset state of thecharge detector 102 is cancelled (off) during a reading period in whichthe charge detector 102 reads a pixel signal.

The timing generator 14 turns on a transfer signal (TS) to transfer theelectric charge in the PD 100 to the charge detector 102 while the resetstate of the charge detector 102 remains cancelled. The charge detector102 converts the electric charge into voltage.

Subsequently, the timing generator 14 turns on a switch control signal(S) that controls a switch 104 to send the image signal converted into avoltage signal to the analog bus. Outputs from all the pixels areconnected to the analog bus. One selected pixel is connected to theanalog bus at a certain timing while the other pixels are disconnectedfrom the analog bus by the switches 104. All the pixel signals in theCMOS linear sensor 10 pass a common analog bus as described above.

The image signal output to the analog bus is output to the outside viathe output buffer 106. The timing generator 14 turns off the switchcontrol signal (S) to turn off the switch 104, and the process proceedsto the next pixel. The timing generator 14 continues a series ofprocesses described above until all the pixel signals are output. Thus,each timing at which TS[n], RS[n], and S[n] are turned on is differentby one pixel period, and the series of processes are repeatedapproximately 7000 times in one line period. The CMOS linear sensor 10configured to output image signals in the three RGB colors includesthree analog buses for the three RGB colors.

lsync is a line synchronization signal indicating a period for scanningone main scanning line of image data. The image reading device 1sequentially converts, by the AFE 12, analog image data output from theCMOS linear sensor 10 into digital image data, such as high-speed serialsignals, and outputs the digital image data to the following stage.

The above-described processes are performed on all the pixels of theCMOS linear sensor 10, and the timing generator 14 drives the pixels ata pixel frequency at several megahertz to dozens of megahertz. The CMOSlinear sensor 10 drives operations of one clock of the pixel frequency7000 times (drives the operations using 7000 signals). In order tooperate the CMOS linear sensor 10 faster, impedance needs to be reducedby increasing the size of the switches 104 to prevent the distortion ofa signal waveform, and the analog bus needs to be widened that transfersthe analog signals output from the 7000 pixels. When, however, the sizeof the switches 104 is increased to achieve high-speed operation,parasitic capacitance increases. When the analog bus is widened, wirecapacitance increases. This configuration results in the weakening ofthe signal waveform, thereby preventing the high-speed operation.

First Embodiment

Described next is an image sensing device according to a firstembodiment of the present invention. FIG. 3 is a diagram illustrating anexample of a configuration outline of an image sensing device 20according to the first embodiment. The image sensing device 20 is a CMOScolor liner sensor configured to read, for example, Pix1 to Pix(n) thatare pixel positions on a subject in the three RGB colors, and includes npixels (pixel units) in each color arranged in one direction. In thefollowing description, the same reference signs are given tosubstantially the same constituent elements of each image sensingdevice.

A pixel 200 provided with an R filter (not illustrated) includes aphotodiode (PD_r) and a pixel block (pixblk_r). A pixel 202 providedwith a G filter (not illustrated) includes a photodiode (PD_g) and apixel block (pixblk_g). A pixel 204 provided with a B filter (notillustrated) includes a photodiode (PD_b) and a pixel block (pixblk_b).Each pixel block includes a charge detector (Cfd) (not illustrated) thatconverts electric charge accumulated in the photodiode (photoelectricconversion element) into voltage, and a circuit that drives the Cfd. Inthe following description, the photodiode may be referred to as PD_*,and the pixel block may be referred to as pixblk_*. The asterisk (*)indicates any one of the colors r, g, and b.

The image sensing device 20 includes n pixels 200, n pixels 202, npixels 204, and n AD converters (ADC). The n ADCs perform analog-digital(A/D) conversion to output image signals to a parallel-serial converter(PS) 206, and the parallel-serial converter (PS) 206 outputs serialdigital signals in each color.

For example, the image sensing device 20 accumulates reflected light(incident light) from a document in the PD_* as electric charge, andconverts the accumulated electric charge into voltage at the Cfd of thepixblk_*. The image sensing device 20 converts analog image signalsoutput from pixel groups each composed of a plurality of pixels intodigital image signals at common ADCs adjacent to the respective pixelgroups. The phrase “adjacent to the respective pixel groups” indicates,for example, a distance in which signals can be transmitted within acertain time period, that is, a distance in which each pixelconstituting a pixel group can transmit a signal to the ADC within atime period without falling behind the other pixels by a couple ofdigits (or by more than double digits).

Each pixel group of the image sensing device 20 is composed of threepixels (pixels surrounded by the black bold line in FIG. 3) in the samecolor adjacent to each other arranged in a direction (main-scanningdirection) in which pixels in each color are arranged, and each pixelgroup uses one ADC (common ADC). In other words, the image sensingdevice 20 immediately converts an analog signal output from the Cfd of apixblk_* into a digital signal at an adjacent ADC. With thisconfiguration, the length of the analog bus can be far shorter, therebyenabling high-speed operation.

All the ADCs in the image sensing device 20 simultaneously convertanalog image signals output from every pixel of all the pixel groupsinto digital image signals. Image data of parallel digital signalsoutput from the ADCs for the respective pixel groups in the imagesensing device 20 is converted into serial data (Dout(r), Dout(g),Dout(b)) at the parallel-serial converter 206, and the serial data isoutput to the following stage.

The number of pixels constituting (selected as) each pixel group of theimage sensing device 20 is not limited to three. For example, the numberof pixels constituting each pixel group may be six (two pixels, an EVENpixel and an ODD pixel, for each RGB color) to use one ADC in common asin the case in which one line is divided into two, even pixels and oddpixels, to output image data.

FIG. 4 is a diagram illustrating a configuration of pixels illustratedin FIG. 3. While FIG. 3 illustrates an example in which each pixel groupis composed of three pixels in the same color and parallel processing isperformed on the pixel groups, FIG. 4 specifically illustrates a pixelgroup in the B color in the image sensing device 20.

Vdd is power supply voltage supplied to the image sensing device 20, andis used as an output reference potential. The PD_bs accumulate electriccharge in accordance with the intensity of incident light. Reset signals(RS1, RS2, RS3) reset the respective charge detectors (Cfds) thatconvert the electric charge accumulated in the PD_bs into voltage.Transfer signals (TS1, TS2, TS3) transfer the electric chargeaccumulated in the PD_bs to the Cfds at which the electric charge isconverted into voltage.

In FIG. 4, the areas including the corresponding Cfd and defined by thedotted line are pixel circuits (pixblk_bs). Analog signals (A_sig_b1,A_sig_b2, A_sig_b3) converted into voltage at the pixblk_bs aretransferred to an ADC adjacent to the pixels 204 (PD_bs and pixblk_bs)in accordance with transfer signals (ADTS1, ADTS2, ADTS3).

In the image sensing device 20, each signal (RS, TS, ADTS) is input toall the pixel groups in parallel. The signals (RS, TS, ADTS) are used incommon among the pixel groups.

FIG. 5 is a diagram illustrating the periphery of an AD converter (ADC)that converts analog signals output from the pixels illustrated in FIG.3 into digital signals. The analog signals (A_sig_b1, A_sig_b2,A_sig_b3) output from the pixels 204 are transferred to the ADC inaccordance with three transfer signals (ADTS1, ADTS2, ADTS3) withdifferent transfer timings.

The analog image signals transferred to the ADC are converted intodigital image signals pixel by pixel while a signal ADEN that enablesthe ADC is high, and the digital signals (D_sig_b1, D_sig_b2, D_sig_b3)are output to the parallel-serial converter 206 while the transfersignals (ADTS1, ADTS2, ADTS3) are high.

The image sensing device 20 can simultaneously transfer the analogsignals A_sig_b1, A_sig_b2, and A_sig_b3 to the ADCs when analogmemories (storage units) are provided at the preceding stages of therespective ADCs. This configuration enables the image sensing device 20to read the same position (pixel) on a subject in each color at the sametime (global shutter).

FIG. 6 is a timing chart illustrating operations for driving the imagesensing device 20. Drive signals for the image sensing device 20 aregenerated by, for example, the timing generator 14 by using thereference clock (CLK) as in the case of the CMOS linear sensor 10illustrated in FIG. 2.

lsync is a line synchronization signal indicating one line period in themain-scanning direction of image data. Because each pixel group of theimage sensing device 20 is composed of three pixels, the timinggenerator 14 first turns on RS1 to reset the corresponding Cfd beforestarting on a line. The timing generator 14 then turns on RS2 at atiming different from the timing at which RS1 is turned on, and turns onRS3 at a timing different from the timings at which RS1 and RS2 areturned on, thereby resetting the three Cfds in the pixel group.

The timing generator 14 sequentially turns on TS1 to TS3 at differenttimings after resetting the Cfds to transfer the electric chargeaccumulated in the PD_* to the Cfds. The timing generator 14 thensequentially turns on ADTS1 to ADTS3 at different timings to input, tothe ADCs, analog signals obtained by converting electric charge intovoltage at the Cfds.

The image sensing device 20 performs the above-described operations atthe same time for each of the pixel groups. Each ADC repeats A/Dconversion, for example, approximately ten times to output 10 bit datawhile the ADEN is high. Image signals converted into digital signals areconverted from parallel digital signals to serial digital signals at theparallel-serial converter 206 and are output to an image processing unit(not illustrated) at the following stage. The number of times theabove-described A/D conversion is performed is not limited to ten, butmay be changed depending on the volume of data necessary for the imagedata received by the image processing unit at the following stage.

FIG. 7 is a schematic diagram illustrating the colors of an image readand reproduced by the image sensing device 20. As described above, eachpixel group of the image sensing device 20 is composed of three pixelsin the same color adjacent to each other arranged in a direction inwhich pixels in each color are arranged, and uses one ADC in common.This configuration enables the image sensing device 20 to performhigh-speed image reading. This configuration may, however, fail toreproduce the color of a read image with high fidelity.

The image sensing device 20 includes one common processing circuit(assuming that the processing circuit is the ADC) for each pixel groupto achieve high-speed image reading and performs parallel processing.Each pixel group in the image sensing device 20 is composed of aplurality of pixels in the same color arranged in an array in themain-scanning direction. This configuration causes fixed pattern noisewhen individual ADCs have different characteristics.

The fixed pattern noise occurring on a black part (dark part) and on awhite part (bright part) of a read image can be compensated by the blackshading correction method and the white shading correction method. When,however, the fixed pattern noise is attributable to a difference inlinearity between ADCs, the effects of the fixed pattern noise appear inhalf tone. Thus, it is difficult to compensate all the effects of thefixed pattern noise by the black shading correction method and the whiteshading correction method described above.

When the image sensing device 20 is used to read an image, the pixels200, the pixels 202, and the pixels 204 can acquire image data at thesame positions in the main-scanning direction (a pixel at the sameposition on the subject such as a pixel at the position of Pix1) byphysically moving a subject or the image sensing device 20 itself. Inthis case, when a gray document (half tone between black and white)having a uniform density among the RGB colors is read, no hue differenceoccurs among three pixels of R, three pixels of G, or three pixels of B.This is because the pixels in each color use the same ADC in common andthus they have the same (common) linearity.

However, uneven color or false color appears among the RGB colors at thesame pixel position, that is, appears on an image obtained bysynthesizing the RGB colors (for example, an image at the position ofPix1 in the main-scanning direction) because the three ADCs havedifferent characteristics. If the ADCs have the same linearity, unevencolor or false color does not appear. However, as long as each ADC is aphysically different circuit, a difference in linearity can occurbetween the ADCs. The linearity can be compensated pixel by pixel, but alarge compensation circuit is required for this purpose and the controlof this circuit is complicated.

Second Embodiment

Described next is an image sensing device according to a secondembodiment of the present invention. FIG. 8 is a diagram illustrating anexample of a configuration outline of an image sensing device 30according to the second embodiment. The image sensing device 30 is aCMOS color linear sensor configured to read, for example, Pix1 to Pix(n)that are pixel positions on a subject in the three RGB colors, andincludes n pixels (pixel units) in each color arranged in one direction.

Each pixel group of the image sensing device 20 illustrated in FIG. 3 iscomposed of three pixels in the same color adjacent to each otherarranged in a direction in which pixels in each color are arranged. Thepixel groups of the image sensing device 30 are configured differentlyfrom those of the image sensing device 20. Each pixel group of the imagesensing device 30 is composed of pixels in all colors (pixels surroundedby the black bold line in FIG. 8) configured to read a subject at thesame position in a direction (main-scanning direction) in which pixelsin each color are arranged, and uses one ADC (common ADC). In otherwords, each pixel group of the image sensing device 30 is composed of aplurality of pixels in all colors (three pixels in the RGB colors in thesecond embodiment) configured to read a subject at the same position byphysically moving the subject or the image sensing device 30 itself. Thenumber of pixels constituting one pixel group of the image sensingdevice 30 is not limited to three. For example, the number of pixelsconstituting one pixel group of the image sensing device 30 may be six(three pixels in the RGB colors×2).

FIG. 9 is a diagram illustrating a configuration of pixels illustratedin FIG. 8. RS1 is a signal that resets the charge detectors (Cdfs) thatconvert electric charge accumulated in the respective PD_rs intovoltage. RS2 is a signal that resets the charge detectors (Cdfs) thatconvert electric charge accumulated in the respective PD_gs intovoltage. RS3 is a signal that resets the charge detectors (Cdfs) thatconvert electric charge accumulated in the respective PD_bs intovoltage.

TS1 transmits electric charge accumulated in the PD_rs to the chargedetectors (Cfds) that convert the electric charge into voltage. TS2transmits electric charge accumulated in the PD_gs to the chargedetectors (Cfds) that convert the electric charge into voltage. TS3transmits electric charge accumulated in the PD_bs to the chargedetectors (Cfds) that convert the electric charge into voltage.

Analog signals (A_sig_r, A_sig_g, A_sig_b) obtained by convertingelectric charge into voltage at the pixblk_rs, the pixblk_gs, and thepixblk_bs are transferred to the ADCs in accordance with differenttransfer signals (ADTS1, ADTS2, ADTS3).

Although the image sensing device 20 and the image sensing device 30have different configurations with respect to the pixel groups, the bothperform parallel processing on the pixel groups including three pixelseach. Thus, the image sensing device 20 and the image sensing device 30both require the signals (RS, TS, ADTS) for each pixel in one pixelgroup. The signals (RS, TS, ADTS) are used in common among the pixelgroups.

FIG. 10 is a diagram illustrating the periphery of an AD converter (ADC)that converts analog signals output from the pixels illustrated in FIG.8 into digital signals. The analog signals (A_sig_r, A_sig_g, A_sig_b)output from the pixel 200, the pixel 202, and the pixel 204,respectively, are transferred to the corresponding ADC while thetransfer signals (ADTS1, ADTS2, ADTS 3) with different transfer timingsare high.

The analog image signals transferred to the ADC are converted intodigital signals pixel by pixel while a signal ADEN that enables the ADCis high, and the digital signals (D_sig_r, D_sig_g, D_sig_b) are outputto the parallel-serial converter 206 while the transfer signals (ADTS1,ADTS2, ADTS3) are high.

The timing at which the image sensing device 30 is driven is the same asthat of the image sensing device 20 as illustrated in FIG. 6 (adifferent RGB color is processed because of the different configurationof the pixel groups).

FIG. 11 is a schematic diagram illustrating colors of an image read andreproduced by the image sensing device 30. As described above, eachpixel group of the image sensing device 30 is composed of pixels in allcolors configured to read a subject at the same position in a directionin which pixels in each color are arranged. Accordingly, the linearityof the ADCs is common (the same) whose effects appear on image data readby the pixels 200, the pixels 202, and the pixels 204 at the sameposition on a subject. In other words, the image sensing device 30 canprevent uneven color or false color from appearing that are caused bythe fixed pattern noise in half tone that cannot be compensated by theblack shading correction method or the white shading correction method.

Third Embodiment

Described next is an image sensing device according to a thirdembodiment in the present invention. FIG. 12 is a diagram illustratingan example of a configuration outline of an image sensing device 40according to the third embodiment. FIG. 13 is a diagram illustrating theperiphery of an AD converter (ADC) that converts analog signals outputfrom the pixels illustrated in FIG. 12 into digital signals. The imagesensing device 40 is configured such that programmable gain amplifiers(PGA) are provided at the preceding stages of the respective ADCs forthe pixel groups of the image sensing device 30 illustrated in FIG. 8.Each PGA is configured to change the amplification factor for the PD_*sthat constitute a pixel group. The PGAs amplify analog signals outputfrom the pixels 200, the pixels 202, and the pixels 204, whereby theimage sensing device 40 can use the dynamic range of the ADCsefficiently.

The PGAs may amplify the analog signals output from the pixels 200, thepixels 202, and the pixels 204 at different amplification factors. Thisconfiguration can optimize the dynamic range in each color even if thelevels of analog signals are different for each RGB color.

FIG. 14 is a timing chart illustrating operations for driving the imagesensing device 40. Drive signals for the image sensing device 40 aregenerated by, for example, the timing generator 14 by using thereference clock (CLK) as in the case of the CMOS linear sensor 10illustrated in FIG. 2. The image sensing device 40 is provided with thePGAs at the respective positions between the pixel groups and the ADCs.Analog signals are transferred from the Cdfs to the PGAs while TS ishigh. The analog signals transferred to the PGAs are amplified whilePGEN is high and are input to the ADCs. The amplified analog signalsinput to the ADCs are converted into digital signals while ADEN is high.

Fourth Embodiment

Described next is an image sensing device according to a fourthembodiment of the present invention. FIG. 15 is a diagram illustratingan example of a configuration outline of an image sensing device 45according to the fourth embodiment. FIG. 16 is a diagram illustrating aconfiguration of the pixels illustrated in FIG. 15. FIG. 17 is a diagramillustrating the periphery of an AD converter (ADC) that converts analogsignals output from the pixels illustrated in FIG. 15 into digitalsignals. The image sensing device 45 is configured such that analogmemories (mem_rs) 210, analog memories (mem_gs) 212, and analog memories(mem_bs) 214 are provided for the respective pixels (the pixels 200, thepixels 202, and the pixels 204) of the image sensing device 30illustrated in FIG. 8. The image sensing device 45 includes a timinggenerator (TG) 216 that has a function of controlling the analogmemories 210, 212, and 214 to store therein outputs from the pixels ineach pixel group in addition to the function that the timing generator14 has.

FIG. 18 is a timing chart illustrating operations for driving the imagesensing device 45. Drive signals for driving each unit of the imagesensing device 45 are generated by the timing generator 216. The imagesensing device 45 stores image signals output from the pixels (thepixels 200, the pixels 202, the pixels 204) in the analog memories 210,212, and 214, respectively, while a signal Sig_ST is high and a signalMem_EM is high. In other words, the image sensing device 45 can storethe analog signals A_sig_r, A_sig_g, and A_sig_b in the analog memoriesunder the control of the timing generator 216, thereby achievingsimultaneous exposure (global shutter) by which RGB pixels are exposedat the same timing. This configuration enables the image sensing device45 to read the subject at the same position (pixel) in each color at thesame time, thereby preventing color shift.

Comparative Example

Described next is a comparative example of an image sensing device. FIG.19 is a diagram illustrating a configuration outline of a CMOS areasensor 11 according to the comparative example. The CMOS area sensor 11includes the pixels 200, the pixels 202, and the pixels 204 that arearranged two-dimensionally (in the main-scanning direction and in thesub-scanning direction) to form, for example, the Bayer arrangement. TheCMOS area sensor 11 includes an AD converter (ADC) 110 provided for eachcolumn, for example. FIG. 19 illustrates the CMOS area sensor 11,focusing on pixels and a processing circuit (ADC in the comparativeexample) that have different features from the CMOS linear sensor.

The CMOS area sensor 11 reads any one of R, G, and B colors asinformation per pixel (one pixel=one color) at the same position on asubject (the pixel position on the subject). Information on the othertwo colors needed for a pixel at the same position on the subject (thepixel position on the subject) is generated by an interpolationprocedure using information on the peripheral pixels.

Even though the CMOS area sensor 11 uses one ADC in common for eachpixel group including a plurality of pixels (for example, pixels in eachcolumn), because values of peripheral pixels using different ADCs areused in the interpolation procedure, uneven color or false color appearson an image due to different characteristics of the individual ADCs. Forthis reason, the effects of the embodiments described above areparticular to the CMOS linear sensors.

Described next is an image forming apparatus provided with an imagereading device including the image sensing device according to any oneof the embodiments. FIG. 20 is a diagram illustrating an outline of animage forming apparatus 50 including an image reading device 60including, for example, the image sensing device 45. The image formingapparatus 50 is, for example, a copier or a multifunction peripheral(MFP) including the image reading device 60 and an image forming unit70.

The image reading device 60 includes, for example, the image sensingdevice 45, a light-emitting diode (LED) driver (LED_DRV) 600, and an LED602. The LED driver 600 drives the LED 602 in synchronization with, forexample, a line synchronization signal output from the timing generator(TG) 216. The LED 602 irradiates a document with light. Insynchronization with the line synchronization signal, for example, theimage sensing device 45 receives light reflected on the document and aplurality of PD_*s (not illustrated) generate electric charge and startaccumulating it. After performing AD conversion and parallel-serialconversion, for example, the image sensing device 45 outputs theresulting image data to the image forming unit 70.

The image forming unit 70 includes a processing unit 80 and a printerengine 82. The processing unit 80 and the printer engine 82 areconnected with each other via an interface (I/F) 84.

The processing unit 80 includes an LVDS 800, an image processing unit802, and a central processing unit (CPU) 804. The CPU 804 controlsunits, such as the image sensing device 45, that constitute the imageforming apparatus 50. The CPU 804 (or the timing generator 216) controlsthe PD_*s to start generating electric charge at substantially the sametime in accordance with the amount of received light.

The image sensing device 45 outputs image data of an image read by, forexample, the image reading device 60, the line synchronization signal,and a transmission clock to the LVDS 800. The LVDS 800 converts, forexample, the received image data, line synchronization signal, andtransmission clock into parallel 10 bit data. The image processing unit802 performs image processing by using the converted 10 bit data, andoutputs the resulting image data to the printer engine 82. The printerengine 82 prints a document by using the received image data.

As described above, the image sensing device according to any one of theembodiments includes an ADC that performs A/D conversion for each pixelgroup composed of a plurality of pixels and that is disposed in aposition adjacent to the pixel group. This configuration can reduce wireresistance and wire capacitance along the analog bus, thereby enablingthe image sensing device to read an image faster. In other words, theimage sensing device according to any one of the embodiments can alsoreduce drive frequencies of analog signals.

According to the present embodiments, it is possible to achievehigh-speed image reading.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. An image sensing device comprising: a pluralityof photoelectric conversion elements arranged in a line direction foreach color of received light, the photoelectric conversion elements ofone color being arranged in one line; and an analog-digital (AD)converter that performs analog-digital conversion for each pixel groupconfigured by a plurality of photoelectric conversion elements selectedfrom the photoelectric conversion elements, the AD converter beingdisposed in a position adjacent to each of the photoelectric conversionelements configuring the pixel group, each pixel group includingphotoelectric conversion elements for three different colors.
 2. Theimage sensing device according to claim 1, wherein the pixel group isconfigured by the photoelectric conversion elements in the threedifferent colors of the received the photoelectric conversion elementsbeing configured to sequentially perform photoelectric conversion pixelby pixel.
 3. The image sensing device according to claim 1, furthercomprising: a controller that controls the photoelectric conversionelements of a pixel group to simultaneously perform photoelectricconversion; and a storage that stores results of the photoelectricconversion simultaneously performed by the photoelectric conversionelements.
 4. The image sensing device according to claim 1, furthercomprising: an amplifier disposed at a preceding stage of the ADconverter, the amplifier amplifying a signal.
 5. The image sensingdevice according to claim 4, wherein the amplifier is configured tochange an amplification factor for each of the photoelectric conversionelements configuring the pixel group.
 6. An image reading device,comprising: the image sensing device of claim
 1. 7. An image formingapparatus, comprising: the image reading device of claim 6; andcircuitry configured to form an image read by the image reading device.8. The image sensing device according to claim 1, wherein the threedifferent colors correspond to R, G, B colors, and the AD converterperforms the analog-digital conversion for each pixel group thatincludes photoelectric conversion elements in the R, G, B colors.
 9. Theimage sensing device according to claim 1, wherein the three differentcolors correspond to R, G, B colors, the plurality of photoelectricconversion elements is arranged in parallel to the line direction foreach R, G, B color, and the each pixel group includes photoelectricconversion elements of R, G, B colors in a vertical direction to theline direction.
 10. The image sensing device according to claim 1,wherein the pixel group is configured by the photoelectric conversionelements in each color of the received light, the photoelectricconversion elements being configured to sequentially performphotoelectric conversion pixel by pixel.
 11. An image sensing methodperformed by an image sensing device comprising a plurality ofphotoelectric conversion elements arranged in a line direction for eachcolor of received light, the method comprising: performing, by ananalog-digital (AD) converter, analog-digital conversion for each pixelgroup configured by a plurality of photoelectric conversion elementsselected from the photoelectric conversion elements, the photoelectricconversion elements of one color being arranged in one line, the ADconverter being disposed in a position adjacent to each of thephotoelectric conversion elements configuring the pixel group, eachpixel group including photoelectric conversion elements for threedifferent colors.
 12. An image sensing device comprising: a plurality ofphotoelectric conversion means arranged in a line direction for eachcolor of received light, the photoelectric conversion means of one colorbeing arranged in one line; and analog-digital (AD) conversion means forperforming analog-digital conversion for each pixel group configured bya plurality of photoelectric conversion means selected from theplurality of photoelectric conversion means, the AD conversion meansbeing disposed in a position adjacent to each of the plurality ofphotoelectric conversion means configuring the pixel group, each pixelgroup including photoelectric conversion means for three differentcolors.
 13. The image sensing device according to claim 12, wherein thepixel group is configured by the photoelectric conversion means in thethree different colors of the received light, the photoelectricconversion means for sequentially perform photoelectric conversion pixelby pixel.
 14. The image sensing device according to claim 12, furthercomprising: controlling means for controlling the photoelectricconversion means of a pixel group to simultaneously performphotoelectric conversion; and storage means for storing results of thephotoelectric conversion simultaneously performed by the photoelectricconversion means.
 15. The image sensing device according to claim 12,further comprising: amplification means disposed at a preceding stage ofthe AD conversion means, the amplification means amplifying a signal,the amplification means being for changing an amplification factor foreach of the photoelectric conversion means configuring the pixel group.